1. Field of the Invention
The present invention relates to a receiving apparatus, a receiving method, a program, and a receiving system. More particularly, the invention relates to a receiving apparatus, a receiving method, a program, and a receiving system for performing a time deinterleaving process suitable for DVB-T.2-compatible receivers.
2. Description of the Related Art
Communication systems perform reliable communications over noise-plagued communication channels by resorting to coding. For example, wireless systems such as satellite-based networks are exposed to numerous noise sources due to geographical and environmental factors. Such communication channels represent fixed capacities which are defined in terms of the number of bits per symbol at a given signal-to-noise ratio (SNR) and which constitute a theoretical upper limit known as the Shannon limit. As a result, coding design aims at attaining rates that approach the Shannon limit. This aim is closely related to limited bandwidth satellite-based systems.
Recent years have witnessed the development of coding techniques known as turbo coding which help to achieve performance levels getting close to the Shannon limit. Specifically, the developed techniques include Parallel Concatenated Convolutional Codes (PCCC) and Serially Concatenated Convolutional Codes (SCCC). Apart from these turbo coding techniques, Low Density Parity Check Codes (called LDPC coding hereunder), a traditional coding technique known from long ago, are again attracting attention today.
LDPC coding was first proposed by R. G. Gallager in “Low Density Parity Check Codes,” Cambridge, Mass.: M. I. T. Press, 1963. Later, the technique once again drew attention when discussed illustratively by D. J. C. MacKay in “Good error correcting codes based on very parse matrices,” submitted to IEEE Trans. Inf. Theory, IT-45, pp. 399-431, 1999, and by M. G. Luby, M. Mitzenmacher, M. A. Shokrollahi and D. A. Spielman, in “Analysis of low density codes and improved designs using irregular graphs,” in Proceedings of ACM Symposium on Theory of Computing, pp. 249-258, 1998.
Studies in recent years have made it increasingly clear that LDPC coding, when its code length is prolonged, provides performance levels approaching the Shannon limit like turbo coding. Because its minimum distance is proportional to its code length, LDPC coding offers an excellent block error rate and develops few so-called error floor phenomena, which can be observed in decoding characteristic by turbo coding arrangements.
The above-mentioned advantages of LDPC coding have led to the adoption of this coding technique into DVB (Digital Video Broadcasting)-T.2 (DVB BlueBook A122 Rev. 1, Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2), searched for on Mar. 17, 2009 at the DVB site dated Sep. 1, 2008<URL: http://www.dvb.org/technology/standards/> (Non-Patent Document 1)). That is, DVB-T.2 is the second generation digital terrestrial TV broadcasting standard being deliberated on (as of March 2009) by ETSI (European Telecommunication Standard Institute).
The DVB-T.2-compatible receiver incorporates a time deinterleaver. That is, the signal input to the receiver has undergone a block interleaving process (time interleaving process) performed across a plurality of LDPC codes on the transmitting side. This process is carried out in units of cells (in units of constellations in this case). Thus the time deinterleaver performs a deinterleaving process corresponding to the time interleaving process on the input signal.
Specifically, the time deinterleaver may have a memory that stores “a” cells in the column direction and “b” cells in the row direction. Thus the time deinterleaver performs the time deinterleaving process by writing supplied cell data successively to a predetermined address of the memory in units of N cell data (N is an integer of at least 1) and by reading out successively the written cell data from the same address.
In the description that follows, each storage area which is one cell long in the row direction and which extends in the column direction will be called a column. Also, the number of units N in which cell data are written by the time deinterleaver will be called the column count N in the ensuing description.